Automatic cycle machine tool



Dec. 1, 1953 H. c. KEMPER E'TAL 2,660,932

AUTOMATIC CYCLE MACHINE TOOL Filed Oct. 15, 1951 HAND AUTO. 73

INVENTORS. HARRY 6. KEMPER AND NELSON 0. COOPER A TTORNE).

Patented Dec. 1, 1953 UNITED STATES PATENT OFFICE.

AUTOMATIC CYCLE MACHINE TOOL Delaware Application October 15, 1951, Serial No. 251,402

7 Claims. 1

This invention pertains to improvements in automatic operating cycles for machine tools.

One of the objects of this invention is to provide an improved control circuit for a machine tool having relative rapid traverse and feeding movements between work and tool.

Another object of this invention is to provide an improved control and operating circuit for a machine tool for effecting rapid traverse and feeding movements between work and tool in a predetermined operating cycle.

Still another object of this invention is to provide an improved feed and rapid traverse mechanism for a machine tool which is fully automatic and fool proof in operation and yet readily adapted to manual control when desired.

Still another object of this invention is to provide an improved milling machine transmission and control mechanism for actuating the work table at feed and rapid traverse movements.

Further features and advantages of this invention will appear from a detailed description of the drawing in which the figure of the drawing shows a diagrammatic circuit layout applied to a machine tool incorporating the features of this invention.

As illustrative of one form of machine tool to which the aforementioned control circuit is especially adapted, there is illustrated a typical milling machine having the main column It containing the cutter spindle II and having a suitable milling cutter l2 mounted thereon. A suitable transmission in the column II] for driving the spindle i I and cutter i2 is actuated from the input drive pulley 13 connected by suitable belts l4 and the motor pulley It to the main spindle drive motor i5. Associated with the spindle drive motor I6 is a suitable magnetic brake ll for quickly arresting rotation of the motor it when de-energized and the cutter spindle H and cutter 12 through the transmission mechanism in the column IE.

Mounted for the usual reciprocatory motion on the column H3 is the work table l8 which is actuated in a well known manner by the feed screw 19 which is connected to be driven in one direction or the other by a clutch spool 20 slidingly mounted relative to the screw l9 but in driving relation therewith, the clutch spool .20

having clutching means 2i and 22 adapted to engage mating clutching means on the bevel drive pinions 23 and 24, each of which pinions are driven in opposite directions by the common drive bevel gear 25 which in turn is driven as illustrated diagrammatically at 26, from the in the diagram. The motions thus discussed are the slow feed motions for the work table during the actual engagement of the cutter 12 with a workpiece mounted on the work table it.

It is also desirable to actuate the work table in either direction at a fast or rapid traverse motion so as to bring the work and cutter into relative operating position as promptly as possible and to also retract them from one another as fast as practicable as soon as the cutting operation has been completed so as to save unnecessary time of noncutting operations at the slow feeding speed. This is accomplished by means of a rapid traverse drive motor 2? which is mounted on the table M by a suitable bracket 28 and has a motor drive shaft 29 carrying a drive pinion 30 which in turn is connected to a gear 3| fixed to the feed screw 19 so that the armature of the motor 27 is at all times positively and directly connected to the feed screw 19.

Power for energizing the main drive spindle motor I6 is derived from a suitable source of three phase alternating current such as the leads Li, L2 and L3 to which are connected the leads 5?? which in turn are connected through the leads 33 the contacts Sc and the leads E i to the motor IS. The rapid traverse motor is connected to the leads 32 through the leads 35, 36, normally open forward rapid traverse power contacts 'IFa and leads 37, for forward actuation of the motor 2'! and work table I8 at rapid traverse movement. For reverse operation of the rapid traverse motor 21 and retraction of the table l8, leads .35 are connected through leads 3&3 normally open reverse rapid traverse power controls contacts Tits and leads 39 to the power supply leads 32.

The clutch member 25) is actuated manually for engaging and disengaging the feed for one di rection .or the other of feed movement of the table l8 by the feed control lever it which is pivotally mounted on the column or frame structure of the milling machine in a well known mannerwby a suitable pivot pin il and has a lever arm 42 connected to the clutch spool in such a manner that when the lever 4 is moved from its accuses neutral or stop feed position 40a to the forward feed position we clutch member 20 will be engaged with the bevel pinion 23 for driving feed screw i9 as described to effect forward feeding movement of the table [8. When the feed control lever 4c is moved to the feed reverse position Mic, the clutch member 20 is engaged to be driven from the bevel pinion 24 for reverse feed movement to the table l8 as described.

Operation of the machine in automatic cycle is accomplished follows:

With the worlr table iii in fully retracted or starting position, such as illustrated diagram-- matically at '53 in the diagram on top of the work table it in the drawing, with the manual feed control lever ill in its neutral position ills, a lug it fixed to the lever ill engages the actuating arm $5 or the first limit switch LS2 so as to hold its contact closed interconnecting lead 4? with lead A third limit switch LS3 has its contact i9 held open to disconnect leads till and 51, by means of a trip dog 52 carried on the work table iii which engages the control arm of the third limit switch LS3 at this time. In order to begin the automatic cycle the operator moves the selector switch 5:1 to automatic position so a to interconnect leads and ll. The momentary start contact button is then pressed so to energize control relay coil CR by completing a circuit from power supply lead Ll through lead El, 5%, stop push button lead Gil, and the lead 6| connected to the control relay coil CR, while the other end of the coil CE is connected through the lead iii. to complete the circuit to the other lead L2 of the single phase control circuit Ill-L2. Energizing the control relay coil CR causes the first normally open control relay contact CRa to close to interconnect lead to through lead 63 and lead t l and the closed contact CRo to a lead 65. Lead $5 in turn is connected to lead 66 which is open at second limit switch LS! and first limit switch LS2 at the beginning of the operating cycle. Also, at this time, first normally closed control relay contact (31th is open so as to disconnect lead 5% from lead Lil connected to the relay coil TH which in turn is connected through a lead '68 to the power supply line 69 connected to the lead Ll. Lead 65 is also connected to a lead iii which is open at the selector switch 54 at this time. Further, when the control relay coil CR is energized the second normally open control relay contact CRO is closed to interconnect lead H with lead l2 so as to energize the relay coil S to close contacts SA for energizing and starting up the spindle drive motor Iii. Second normally closed control relay contacts CRd also are opened by energizing control relay coil CR so as to cut out and release the magnetic brake ll for free rotation of the main drive motor ill.

When the start button is pressed its second normally open contact interconnects leads "(3 and "it, lead l5 being connected through lead to the traverse forward relay coil Ti the other end of which coil is connected through a lead l5 to the power supply lead lit. The lead M in turn is connected to a lead ll which at this time is interconnected to the lead through the closed contact l3 of second limit switch LS! and through the lead ill and contact iii of limit switch LS2 and the lead 22', the closed contact or" the selector switch ll l, to leads 55, oil, stop push button 59, and lead to the other power supply lead '1 so as to close normally open forward rapid. traverse powe contacts TFO: to energize the rapid traverse motor ill in forward movement. This forward rapid traverse movement continues until a trip dog to the work table it the control arm lit of second limit switch LSi opening contact and closing contact hi to interconnect lead (35 with lead 8'2 thus ole-energizing the coil TE and opening contacts TFa to ole-energize the rapid traverse motor 2?.

At the conclusion of the rapid traverse movement forward at the point 83 in the diagram on the work table ill in the drawing, the operator then moves the feed control lever til to the forward feed position 4% so as to apply power drive from t1 e column transmission ill to the feed screw it described. In so moving the lever from position lilo to position title the cam lug 4 releases the control arm $5 of the first limit switch LS2 so as to open contacts l6 and close contacts 84 interconnecting leads 32 and (i l. The normal feeding movement of the work table l8 thus continues with the lever 40 in its feed forward position 462) until the point 85 in the aforementioned diagram is reached at the end of the forward feeding cycle. At this time a suitable trip dog 86 fixed on the wor table it engages the operating pin 57 on the projecting lug 8B of the control lever til so as to move it back from its feed forward position tab to its neutral position lilo stopping the feeding motion. It is important to note that so long as contacts :26 are open in the first limit switch LS2 which occurs whenever the lever is moved to a feed position lso or dale, the rapid traverse movement is renders inoperative so that at no time will the rapid traverse motor be energized with the positive feed clutch spool in engagement for one direction or the other of feed travel. Also, the second limit switch LS1 contacts l8 when opened prevent operation of the rapid traverse movement when the operating during its normal forward feeding stroke.

As described above the trip dog 52 on the table it normally holds the contact of the third limit switch LS3 open when the table is -in full retracted position at the start of an operating cycle. However, as soon as the table begins to move forward and the trip dog 52 releases the control a in 53 or the third limit switch LS3 contacts 19 become closed and remain so during the forward and return movements of the work table it. 'lhus at the end of the forward rapid traverse and feeding movements at the point 35 in the diagram contacts t9 are closed.

At the end of the forward feed stroke at the point 85 and with the feed control lever 4i] again moved back to position 40a, contacts M of first limit switch LS2 are opened so as to disconnect lead 66 from lead 6| with the result that the control relay coil CE is ole-energized opening first normally open control relay contact Crtc and closing first normally closed control relay contact CR1). Closing first normally closed control relay contact CR1) interconnects leads 6? with lead through the closed contact ll? or third llmit switch LS3 and lead 48 the contacts ie of first limit switch LS2 to the lead ll and then through the closed contact of the selector switch 54 to the leads 55, stop push button 59 and lead 58 to the power supply lead 5"! so as to shor gize the traverse reverse relay coil TB closin normally open reverse rapid traverse power con tacts TRa to energize the traverse motor 2'! for reverse operation to retract the table from the position 89 in the diagram to the starting position 90 or 43 at the beginning of the cycle just described. As the rapid traverse movement continues from position 89 to position 90, as position 98 is reached the third limit switch LS3 is again operated by the trip dog 52 to open contacts 49 and thereby de-energize the traverse reverse relay coil T c and stop the rapid traverse movement. lhe cycle just described may then be r peated by merely pressing the start button 56 again and the machine functioning and circuit operating as described.

At any these the entire operation of the circuit may be arrested by pressing the stop push button which breaks the connection between the leads 58 and tail. Ihe spindle motor It and magnetic brake ii are respectively ale-energized and energized to arrest rotation of the spindle H at the end of the forward feedingmotion at the points '-E8S by de-energizing the control relay coil CR as described. I

The machine may be-operated in hand manual cycle by moving the selector switch 54 to a position to interconnect lead GI and lead whereupon pressing of the start button 5% and releasing thereof causes the control relay coil CR to remain energized so that the spindle motor I6 is driving and the magnetic brake ll released. By thus disconnecting lead 41 from lead 55 the limit switches LSl, LS2 and LS3 are rendered inoperative and the machine may be controlled in feeding motion by manipulating the control lever 4 and in rapid traverse motion by manipulating the usual hand wheels and bell crank handles for actuating the feed screw I9 is desired. The circuit also arranged to permit jogging of the work spindle and intermittent release of the magnetic brake ill by pressing the jog button Eli which momentarily energizes the relay coil S while deenergizing the magnetic brake I? when pressed to interconnect leads I! and 72 and to disconnect leads t2 and 93 associated with the magnetic brake circuit which is energized from a transformer 94 having a primary winding 95 interconnected to leads 51 and 69 and having a secondary winding 96 connected through a suitable rectifier means 91 and control rheostat 93 to the leads $39 and IE0 connected to the magnetic brake I l in a well known manner.

While the apparatus herein disclosed and described constitutes a preferred form of the ine vention, it is also to be understood that the apparatus is capable of mechanical alteration without departing from the spirit or" the invention and that such mechanical arrangement and commercial adaptation as fall within the scope of the appendent claims are intended to be included herein.

Having thus fully set forth and described this invention what is claimed as new and desired to be obtained by United States Letters Patent is:

1. An automatic cycle control mechanism for a machine tool having, a main drive motor, a movable element, a mechanical feed drive for said movable element, means for driving said mechanical feed drive from said main drive motor, a clutch for connecting or disconnecting said main drive motor relative to said mechanical feed drive, a rapid traverse drive motor directly connected to said mechanical feed drive, a feed control lever manually operable to engage or disengage said clutch, means on said movable element for moving said feed control lever from an engaged position to disengaged position of said clutch, a source of power for operating both of said motors, a start push button, a first limit switch actuated by the movement of said feed control lever when in disengaged position of said 6 clutch to cause said start push button to energize both said motors when pressed, a second limit switch actuated by the movement of said movable element to a predetermined forward position to cause said source or" power to be disconnected from said rapid traverse drive motor, means in said first and second limit switches to maintain connection of said source of power to said main drive motor after said second limit switch has been operated to disconnect power from said rapid traverse drive motor, and means in said first limit switch operable by movement of said feed control lever to disconnected position of said mechanical clutch, after said second limit switch has been actuated to de-energizc said rapid traverse drive motor, to de-energize said main drive motor and energize said rapid traverse drive motor in reverse movement to retract said movable element.

'2. An automatic cycle control mechanism for a machine tool having, a main drive motor, a movable element, a mechanical feed drive for said movable element, means for driving said mechanical feed drive from said main drive motor, a clutch for connecting Or disconnecting said main drive motor relative to said mechanical feed drive, a rapid traverse drive motor directly connected to said mechanical feed drive, a control lever manually operable to engage or disengage said clutch, means on said movable element for moving said feed control lever from an engaged position to disengaged position of clutch, a source of power for operating both of motors, a start push button, a first limit switch actuated by the movement or said feed control lever when in disengaged position of said clutch to cause said start push button to energize both said motors when pre sed, a second limit switch actuated by the movement of said movable element to a predetermined forward position to cause said source of power to be disconnected from said rapid traverse drive motor, means in said first and second limit switches to maintain connection or" said source of power to said main drive motor after said second limit switch has been operated to disconnect power from said rapid traverse drive motor, means in said first limit switch operable by movement or said feed control lever to disconnected position of said mechanical clutch, alter said second limit switch has been actuated to deenergize said rapid traverse drive motor, to die-energize said main drive motor and energize said rapid traverse drive motor in reverse movement to retract said movable element, and a third limit switch actuated by said movable element when in fully retracted position to pie-energize the reverse movement of said rapid traverse drive motor.

3. An automatic cycle control mechanism for a machine tool having, a main drive motor, a movable element, a mechanical feed drive for said movable element, means for driving said mechanical feed drive from said main drive motor, a clutch for connecting or disconnecting sat main drive motor relative to said mechanical feed drive, a rapid traverse drive motor directly connected to said mechanical food drive, a feed control lever manually operable to engage or disengage said clutch, means on movable element ror moving said control lever from an engaged position to disengaged position or said clutch, a source of power for operating both or said motors, a first control circuit connected tosaid source of power, a second control circuit lead connected to said source of power, a norinally closed. stop push button interconnected between said source of power and. said first lead, a start push button having a first normally open contact connected in series with a control relay coil between said first and. second leads, a rapid traverse relay coil connected to actuate normally open forward power contacts connected between said source or power and said rapid traverse olrive motor and. a first normally open traverse forward control contact, a first normally open control relay contact actuated by said control relay c means connecting said first normally open traverse forward and first normally open control relay contacts in series with said first lead. nection between said first normally open cord/act of said start push button and control relay coil, a first limit switch having a normally open ctuable to closed position by inoversiient of; said feed control lever to disengaged position for said clutch shunted across saiiil l'iy open traverse forward control ccntac concl limit switch having a normally ope act actuaole to closecl position i; saiii movable element to a pre- 'eterinined loin arc position shunted across said it lily open traverse iorward control contact, anal a selector switch having a contact 'covable to a pos' ion of direct shunt across first iorinal-iy open traverse contact and both oi normally open limit switch contacts.

An automatic cycle control mechanism :ior chine tool having, a drive motor, a bio elenr t, a mechanical ieecl (irive i'or movable nt, means for driving sairl mechanical drive from said drive motor, a clutch for connecting 'isconnecting main drive motor r ative to said. mechanical lee-d.

"-l traverse drive motor directly coni mechanical food. drive, a feed consally oeerable to engage or disenving s I position to disengaged position to said hitch, a power for operating both or 1 rotors, st control circuit lead connected to said. source oi power, a second control circuit re .1 to source 01 power, a normally c1 button interconnected. be tween source oi power and said first lead, a i a first normally open contact co in s ries with a control relay between. said second leads, a rapid traver coil connected to actuate normally n til contacts connected between cl sou ce of power and said rapid. traverse ve inc anel a first normally open traverse iorwarc. control contact, a first normally open control re'n contact actuated by said control relay coil, I sans connecting first normally open traverse forward and first normally open elay contacts in series with said first mnnection between first normalIy oi start button and said. first limit switch having a contact actuacle to closed position of said .l'eecl control lever to diseni'or said clutch shunted across ope traverse forward control t yitch having a normally open contact aotue to closed position by move-- ment o /able element to a predetermined forward pos n shunted across said first normally open traverse forward control contact, and a selector switch having, a contact movable to a UM'AL,

8 hand position or direct shunt across said first normally open traverse contact and both of said normally open limit switch contacts, a normally closed contact in said first limit switch, a second automatic contact in said selector switch, a norrnally closed contact in said second limit switch actuable to open position by movement of said feed. control lever to disengaged position said clutch, a normally closed contact in saiol second limit switch actnable to open position by move ment or said movable element to sairi pretieter mined forward position, a second normally open start push button contact, traverse forward relay coil, means for connec .ng s second automatic contact of said selector switch, said normally closed contacts or and second. limit switches, said second normally open contact oi said start push button and traverse forward relay coil in series between sairl first and second. leads, and. a seconci normally ope. con trol contactactnateo by traverse forward relay coil shunted. said a normally open start push. 't' iililiill contact.

5. An automatic cycle co l for a machine tool having, c drive motor, a movable element, a niechan ive for movable cl mechanical fees. tor, a clutch connoc g or main drive motor relative to sale drive, a rapid clri've inotor iiirectly conve, feed con e or cliscnti clutch, H1" for ihO/illg said feed control leve caged position. to disengaged po clutch, a source of ower for op rating 2 said. motors, a first coro'i circni' connects to source of po er, a lead. connected. to said start push button having contact connected in series with coil between said first and second. traverse relay coil connected to acts. open forward. power contacts cosaid source of power and. drive motor and a nor forward. control contact, My open control relay c ntact actuacontrol relay coil, me. as connecti e; ormally open traverse i'orwaifi Qwfiii first normally open control relay contacts in series with saic first lead and a connection co-tween said normally open contact of start plSll button and said control relay coil first t switch havin a normally open cJ'tact actoable to closed. posi tion by movement of con rol lever to disengaged position for said chi h shunted across said normally open traverse forward control contact, a seconi. limit switch having a normally open contact actnable to closed position by movement of said rnov element a predetermined forward position shunted. across said.

normally open traverse iorwe control contact, and a selector switch having a contact movable to a car :i position of direct shunt across said. first normally open traverse contact and both of said normally open limit switch contacts, a n rmally closes. contact in first limit we e? position of said clutch, a normally closed contact in said secondlimit switch actuabl'e'to open positio'n by movement of said movable element to said predetermined forward position, a second normally open start push button contact, a traverse forward relay coil, means for connecting said second automatic contact of said selector switch,said normally closed contacts of said first and second limit switches, said second normally open contact of said start push button and said traverse forward relay coil in series between said first and second leads, and a second normally open control contact actuated by said traverse forward relay coil shunted across said second normally open start push button contact, a third limit switch having a normally closed contact held in open position by the movement of said movable member to fully retracted starting position, a first normally closed contact actuated by said control relay coil, traverse reverse relay coil, normally open reverse power contacts connected between said source of power and said rapid traverse drive motor actuated by said traverse reverse relay coil, means for connecting said third limit switch contact, said first normally closed contact of said control relay coil, and said traverse reverse relay coil in series between said second lead and a connection between said normally closed contacts of said first and second limit switches.

6. An automatic cycle control mechanism for a machine tool having, a main drive motor, a movable element, a mechanical feed drive for said movable element, means for driving said mechanical feed drive from said main drive motor, a clutch for connecting or disconnecting said main drive motor relative to said mechanical feed drive, a rapid traverse drive motor directly connected to said mechanical feed drive, a feed control lever manually operable to engage or disengage said clutch, means on said movable element for moving said feed control lever from an engaged position to disengaged position to said clutch, a source of power for operating both of said motors, a first control circuit lead connected to said source of power, a second. control circuit lead connected to said source of power, a normally closed stop push button interconnected between said source of power and said first lead, a start push button having a first normally open contact connected in series with a control relay coil between said first and second leads, a rapid traverse relay coil connected to actuate normally open forward power contacts connected between said source of power and said rapid traverse drive motor and a first normally open traverse forward control contact, a first normally open control relay contact actuated by said control relay coil, means connecting said first normally open traverse forward and first normally open control relay contaste in series with said first lead and a connection between said first normally open contact of said start push button and said control relay coil, a first limit switch having a normally open contact actuable to closed position by movement of said feed control lever to disengaged position for said clutch shunted across said first normally open traverse forward control contact, a second limit switch having a normally open contact actuable to closed position by movement of said movable element to a predetermined forward position shunted across said first normally open traverse forward control contact, and a selector switch having a contact movable to a hand position of direct shunt across said first normally 10 open traverse contact and both of said normally open limit switch contacts, a normally closed contact in said first limit switch, a second automatic contact in said selector switch, a normally closed contactin said second limit switch actuable to open position by movement of said feed control lever to disengaged position of said clutch, a normally closed contact in said second limit switch actuable to open position by movement of said movable element to said predetermined forward position, a second normally open start push button contact, a traverse forward relay coil, means for connecting said second automatic contact of said selector switch, said normally closed contacts of said first and second limit switches, said second normally open contact of said start push button and said traverse forward relay coil in series between said first and second leads, and a second normally open control contact actuated by said traverse forward relay coil shunted across said second normally open start push button contact, a third limit switch having a normally closed contact held in open position by the movement of said movable member to fully retracted starting position, a first normally closed contact actuated by said control relay coil, a traverse reverse relay coil, normally open reverse power contacts connected between said source of power and said rapid traverse drive motor actuated by said traverse reverse relay coil, means for connecting said third limit switch contact, said first normally closed contact of said control relay coil, said traverse reverse relay coil in series between said second lead and a connection between said normally closed contacts of said first and second limit switches, a second normally open contact actuated by said control relay coil, a main drive spindle motor relay coil, power contacts actuable by said main drive spindle motor relay coil connected between said source of power and said spindle motor, and means for connecting said second normally open contact of said control relay coil and said main drive spindle motor relay coil in series between said first and second leads.

7. An automatic cycle control mechanism for a machine tool having, a main drive motor, a movable element, a mechanical feed drive for said movable element, means for driving said mechanical feed drive from said main drive motor, a clutch for connecting or disconnecting said main drive motor relative to said mechanical feed drive, a rapid traverse drive motor directly connected to said mechanical feed drive, a feed control lever manually operable to engage or disengage said clutch, means on said movable ele ment for moving said feed control lever from an engaged position to disengaged position to said clutch, a source of power for operating both of said motors, a first control circuit lead connected to said source of power, a second control circuit lead connected to said source of power, a normally closed stop push button interconnected between said source of power and said first lead, a start push button having a first normally open contact connected in series with a control relay coil between said first and second leads, a rapid traverse relay coil connected to actuate normally open forward power contacts connected between said source of power and said rapid traverse drive motor and a first normally open traverse forward control contact, a first normally open control relay contact actuated by said control relay coil,

connecting said first normally open traverse forward and first normally open control relay contacts in series with said first lead and a con nection between said first normally open contact of said start push button and said control relay coil, a first limit switch having a normally open contact actuable to closed position by movement of said teed control lever to disengaged position for said clutch shunted across said first normally open traverse forward control contact, a second limit switch having a normally open contact actuable to closed position by movement of said movable element to a predetermined forward position shunted across said first normally open traverse forward control contact, and a selector switch having a contact movable to a hand position of direct shunt across said first normally open traverse contact and both of said normally open limit switch contacts, a normally closed contact in said first limit switch, a second automatic contact in said selector switch, a normally closed contact in said second limit switch actuable to open position by movement of said feed contrcl lever to disengaged position of said clutch, a normally closed contact in said second limit switch aotuable to open position by movement of said movable element to said predetermined forward. position, a second normally open start push button contact, a traverse forward relay coil, means for connecting said second automatic contact oi said selector switch, said normally closed contacts of said first and second limit switches,

second normally open contact of said start push button and said traverse forward relay coil in series between said first and second leads, and a second normally open control contact actuated by said traverse forward relay coil shunted across said second normally open start push button contact, a third limit switch having a normally closed contact held in open position by the movement of said movable member to fully retracted starting '12 position, a first normally closed contact actuated by said control relay coil, a traverse reverse relay coil, normally open reverse power contacts con nected between said source of power and said rapid traverse drive motor actuated by said traverse reverse relay coil, means for connecting said third limit switch contact, said first normally closed contact of said control relay coil, said traverse reverse relay coil in series between said second lead and a connection between said normally closed contacts of said first and second limit switches, a second normally open contact actuated by said control relay coil, a main drive spindle motor relay coil, power contacts actuablc by said main drive spindle motor relay coil connected between said source of power and said spindle motor, and means for connecting said seo- 0nd normally open contact of said control relay coil and said main drive spindle motor relay coil in series between said first and second leads, a jog push button having a normally open contact shunted across said second normally open contact oi said control relay coil.

HARRY C. KEMPER.

NELSON D. COOPER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,259,424 Koch Oct. 14, 1941 2,319,253 Penrose May 18, 1943 2,358,746 Tandler et a1 Sept. 19, 1944 2,362,318 Staples Nov. 7, 1944 1 2,421,187 Derungs May 27, 1947 2,498,272 Herchenroeder Feb. 21, 1950 2,558,275 Siekmann et a1 June 26, 1951 

